Semiconductor devices are commonly found in modern electronic products. Semiconductor devices vary in the number and density of electrical components. Discrete semiconductor devices generally contain one type of electrical component, e.g., light emitting diode (LED), small signal transistor, resistor, capacitor, inductor, and power metal oxide semiconductor field effect transistor (MOSFET). Integrated semiconductor devices typically contain hundreds to millions of electrical components. Examples of integrated semiconductor devices include microcontrollers, microprocessors, charged-coupled devices (CCDs), solar cells, and digital micro-mirror devices (DMDs).
Semiconductor devices perform a wide range of functions such as high-speed calculations, transmitting and receiving electromagnetic signals, controlling electronic devices, transforming sunlight to electricity, and creating visual projections for television displays. Semiconductor devices are found in the fields of entertainment, communications, power conversion, networks, computers, and consumer products. Semiconductor devices are also found in military applications, aviation, automotive, industrial controllers, and office equipment.
Semiconductor devices exploit the electrical properties of semiconductor materials. The atomic structure of semiconductor material allows its electrical conductivity to be manipulated by the application of an electric field or base current or through the process of doping. Doping introduces impurities into the semiconductor material to manipulate and control the conductivity of the semiconductor device.
A semiconductor device contains active and passive electrical structures. Active structures, including bipolar and field effect transistors, control the flow of electrical current. By varying levels of doping and application of an electric field or base current, the transistor either promotes or restricts the flow of electrical current. Passive structures, including resistors, capacitors, and inductors, create a relationship between voltage and current necessary to perform a variety of electrical functions. The passive and active structures are electrically connected to form circuits, which enable the semiconductor device to perform high-speed calculations and other useful functions.
Semiconductor devices are generally manufactured using two complex manufacturing processes, i.e., front-end manufacturing, and back-end manufacturing, each involving potentially hundreds of steps. Front-end manufacturing involves the formation of a plurality of die on the surface of a semiconductor wafer. Each die is typically identical and contains circuits formed by electrically connecting active and passive components. Back-end manufacturing involves singulating individual die from the finished wafer and packaging the die to provide structural support and environmental isolation.
One goal of semiconductor manufacturing is to produce smaller semiconductor devices. Smaller devices typically consume less power, have higher performance, and can be produced more efficiently. In addition, smaller semiconductor devices have a smaller footprint, which is desirable for smaller end products. A smaller die size may be achieved by improvements in the front-end process resulting in die with smaller, higher density active and passive components. Back-end processes may result in semiconductor device packages with a smaller footprint by improvements in electrical interconnection and packaging materials.
Another goal of semiconductor manufacturing is to produce higher performance semiconductor devices. Increases in device performance can be accomplished by forming active components that are capable of operating at higher speeds. In high frequency applications, such as radio frequency (RF) wireless communications, integrated passive devices (IPDs) are often contained within the semiconductor device. Examples of IPDs include resistors, capacitors, and inductors. A typical RF system requires multiple IPDs in one or more semiconductor packages to perform the necessary electrical functions.
Baluns (balanced and unbalanced) and RF band-pass filters are important components in wireless communication systems. The balun suppresses electrical noise, performs impedance transformation and matching, and minimizes common-mode noise through electromagnetic coupling. The band-pass filter removes unwanted noise or interference from open air environment and signal paths by passing signals with a designated bandwidth and suppresses signals outside the pass-band.
A conventional RF band-pass filter 10 is shown in FIG. 1 implemented using LC (inductor and capacitor) resonators. An inductor or coil 12 includes first and second end terminals coupled to port 14 and port 16. In one embodiment, port 14 is a single-ended unbalanced port and port 16 is a ground terminal. Alternatively, port 16 is a single-ended unbalanced port and port 14 is the ground terminal. A capacitor 18 is coupled between port 14 and port 16. The inductor 12 and capacitor 18 constitute a first LC resonator. An inductor or coil 20 includes first and second end terminals coupled to balanced ports 22 and 24. A capacitor 26 is coupled between balanced ports 22 and 24. The inductor 20 and capacitor 26 constitute a second LC resonator. An inductor or coil 28 includes end terminals 30 and 32. A capacitor 34 is coupled in series between end terminals 30 and 32 of inductor 28. The inductor 28 and capacitor 34 constitute a third LC resonator. The inductor 28 is formed around a perimeter of inductors 12 and 20 non-overlapping with planar separation. The inductor 28 can have a larger, smaller, or symmetrical value with inductors 12 and 20. The inductors 12 and 20 are the same size and shape, e.g., rectangular, polygonal, or circular, and are wound to create magnetic coupling.
Another conventional RF band-pass filter 36 is shown in FIG. 2. In this case, inductor or coil 37 has first and second end terminals coupled to port 38 and port 39. In one embodiment, port 38 is a single-ended unbalanced port and port 39 is a ground terminal. Alternatively, port 39 is the single-ended unbalanced port and port 38 is the ground terminal. A capacitor 40 is coupled between port 38 and port 39. The inductor 37 and capacitor 40 constitute a first LC resonator. An inductor or coil 41 includes first and second end terminals coupled to balanced ports 42 and 43. A capacitor 44 is coupled between balanced ports 42 and 43. The inductor 41 and capacitor 44 constitute a second LC resonator. An inductor or coil 45 includes end terminals 46 and 47. A capacitor 48 is coupled in series between end terminals 46 and 47 of inductor 41. The inductor 45 and capacitor 48 constitute a third LC resonator. The inductors 37 and 41 overlay inductor 45 with vertical electrical isolation and planar separations. The inductor 45 can have a larger, smaller, or symmetrical value with inductors 37 and 41. The inductors 37 and 41 are the same size and shape, e.g., rectangular, polygonal, or circular, and are wound to create magnetic coupling.
A high attenuation and rejection at the stop-bands and low insertion-loss at pass-band is preferred for optimal signal quality. For example, a WiMAX device in a cellular phone or WiFi application must have sufficient attenuation at the cellular phone band (800 MHz to 2100 MHz) and the WiFi band (4900 MHz to 5900 MHz). However, in a two-port band-pass filter, a balanced state is difficult to achieve. With input coil and output coil being the same size and shape, as described in FIGS. 1 and 2, the impedance transformation ratio is limited for non-50 Ohm matching, e.g., 100 Ohm or complex impedance. In addition, the same-size input and output coil typically cannot achieve the desired high attenuation and rejection response at stop-bands.